• International Journal of Fluid Machinery and Systems
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• 제4권4호
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• pp.387-395
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• 2011

Single-blade centrifugal pumps are widely used as sewage pumps. However, the impeller of a single-blade pump is subjected to strong radial thrust during pump operation because of the geometrical axial asymmetry of the impeller. Therefore, to improve pump reliability, it is necessary to quantitatively understand radial thrust and elucidate the behavior and mechanism of thrust generating. This study investigates the radial thrust acting up on a single-blade centrifugal impeller by conducting experiments and CFD analysis. The results show that the fluctuating component of radial thrust increases as the flow rate deviates from the design flow rate to low or high value. Radial thrust was modeled by a combination of three components, inertia, momentum, and pressure by applying an unsteady conservation of momentum to the impeller. The sum of these components agrees with the radial thrust calculated by integrating the pressure and the shearing stress on the impeller surface. The behavior of each component was shown, and the effects of each component on radial thrust were clarified. The pressure component has the greatest effect on the time-averaged value and the fluctuating component of radial thrust. The time-averaged value of the inertia component is nearly 0, irrespective of the change in the flow rate. However, its fluctuating component has a magnitude nearly comparable with the pressure component at a low flow rate and slightly decreased with the increase in flow rate.

• 한국유체기계학회 논문집
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• 제2권2호
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• pp.5-12
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• 1999

This study presents the measured unsteady flctuation of impeller discharge flow for a centrifugal compressor in an unstable operating region. The characteristics of the blade-to-blade flow at rotating stall onset were investigated by measuring unsteady velocity fluctuations at several different diffuser axial distances using a hot wire anemometer. The flow characteristics in terms of the radial and tangential velocity components and the flow angle distribution at the impeller exit were analyzed using phase-locked ensemble averaging techniques. As a result, increase or decrease of the radial velocity component during the rotating stall is dominated by that of the suction side. The radial velocity distributions show the opposite trends in the regions where the radial velocity during rotating stall onset increases and decreases.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 1998년도 유체기계 연구개발 발표회 논문집
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• pp.129-134
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• 1998

This study presents the measured unsteady fluctuation of impeller discharge flow for a centrifugal compressor in unstable operating region. The characteristics of the blade-to-blade flow at rotating stall onset were investigated by measuring unsteady velocity fluctuations at several different diffuser axial distances using a hot wire anemometer. The flow characteristics in terms of the radial and tangential velocity components and the flow angle distribution at the impeller exit were analyzed using phase-locked ensemble averaging techniques. As a result, increase or decrease of the radial velocity component during the rotating stall is dominated by that on the suction side. The radial velocity distributions show the opposite trends in the regions where the radial velocity during rotating stall onset increases and decreases.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.720-726
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• 2001

Two-dimensional, angle-resolved LDV(Laser Doppler Velocimetry) measurements of the turbulent rotating flow field in a confined cylinder have been performed. The configurations of interest are flows between a rotating upper disk with a rod attached by a disk or impeller(${\theta}= 90^{\circ},\;45^{\circ}$) and a stationary lower disk in a confined cylinder. The mean flow velocity as well as the turbulent intensity of the flow field have been measured. The results show that the flow is strongly dependent on the position of the impellers or the disk, negligibly affected by the Reynolds number in turbulent flow. It is observed that the mixing effect of the axial flow impeller(${\theta}= 45^{\circ}$) is better than that of the radial flow impeller(${\theta}= 90^{\circ}$) or a disk.

• 한국유체기계학회 논문집
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• 제1권1호
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• pp.24-31
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• 1998

Aerodynamic performance tests and flow measurement were carried out for several radial impellers of NACA 65-810 airfoil. The data base obtained are to be used for verifying the methods of flow analysis and CFD codes. The effects of numbers and span of blades on the performances, efficiency and impeller exit flow are investigated in the present study. The flow rate on the performance curve is proportional to the span of the blade for the same value of fan pressure rise. The magnitude of radial velocity component at the impeller exit gradually decreases from the hub to shroud side. The magnitude of tangential velocity component gradually increases from the hub to shroud side. The way of variations of velocity is the same at the diffuser exit, however, becomes more uniform. The pressure rise performance increases with blade number at the small flow coefficients, however, decreases with the number of blade at the large flow coefficients. This shows that flow guidance in important at the low flow rate and the friction becomes significant at the high flow rate.

• 대한기계학회논문집B
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• 제26권5호
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• pp.675-684
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• 2002

Two-dimensional, angle-resolved LDV(Laser Doppler Velocimetry) measurements of the turbulent rotating flow field in a confined cylinder have been performed. The configurations of interest are flows between a rotating upper disk with a rod attached by a disk or impeller($\theta$ = 45$^{\circ}$, 90$^{\circ}$) and a stationary lower disk in a confined cylinder. The mean flow velocity as well as the turbulent intensity of the flow field have been measured. The results show that the flow is strongly dependent on the position of the impellers or the disk, negligibly affected by the Reynolds number in turbulent flow. It is observed that the mixing effect of the axial flow impeller($\theta$ = 45$^{\circ}$) is better than that of the radial flow impeller($\theta$ = 90$^{\circ}$) or a disk.

• 한국산업융합학회 논문집
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• 제4권3호
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• pp.243-251
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• 2001

The effects of various operating parameters(agitation speed, impeller type, antiform agents, impeller spacing etc.) on air-liquid mass transfer was characterized by volumetric mass transfer coefficient($k_La$). Also, the dual-impeller agitated systems are compared with single-impeller agitated systems with a special focus on its applications for bioreactors, $k_La$ was take over a range of 200~450 rpm of agitation speed, and 0.5~2.5 vvm of air flow rates, for four single impeller and impeller combinations consisting of four impeller types, namely rushton, pitched blade, scaba, intermig were tested. The rushton impeller showed the best $k_La$ as compared with other single impellers. The dual impeller system are found to be superior as compared to single impeller in all aspects, The best combination of the dual impeller was a intermig of axial flow type as an upper impeller and a rushton of radial flow type as a lower part. Also, the control of the DO level with the variation of agitation speed was more efficient than that with an increase in air flow rate. The addition of antiform dropped the $k_La$ very large up to 1g/L regardless the type. PPG was less effect on $k_La$ than other antiforms. The impeller spacing and presence of solute are found very effective on $k_La$. When the $NaNO_3$is presented as solute, the $k_La$ increased approximately 50% then control.

• 대한기계학회논문집B
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• 제25권10호
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• pp.1293-1302
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• 2001

It is generally known that radial vane blowers with vaneless diffuser may generate mostly only a rotating stall but backward curved vane blowers may do both an impeller and a diffuser rotating stalls. In this study, it was found from the numerical and experimental results that the diffuser rotating stall does not appear in a radial vane because of the suppression for the diffuser stall appearance by occurring of impeller rotating stall in a large flow rate coefficient. The diffuser rotating stalls occurring when the width of diffuser is broaden fur a backward curved vane blower are classified definitely by the diffuser flow rate coefficient defined by adopting the varying diffuser width.

• 대한기계학회논문집B
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• 제22권9호
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• pp.1247-1254
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• 1998

The vaneless diffusers are widely used in industrial centrifugal compressors which are required to operate within a wide flow range. When very high pressure gases are handled by centrifugal compressor. rotating stall is a serious problem because of the occurance of large aerodynamic exciting forces. Rotating stall mostly often occurs in the impellers but it can occur in vaneless diffusers as well. In this experimental study, the rotating stall in vaneless diffuser with radial type centrifugal impeller was measured by changing the flow rate with I-type, X-type hotwire. As the result, it was cleared which type of rotating stall of the impeller stall would occur and how many stall cells would appear relating with the flow rate. As the flow rate reduced, the propagation speed of rotating stall was reduced. But the stall cell number unchanged with respect to the flow rate.

• 대한기계학회논문집B
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• 제29권7호
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• pp.773-783
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• 2005

Internal flow measurement of very low specific-speed semi-open impellers has been carried out by PIV in order to understand better the internal flow patterns that are responsible fur the unique performance of these centrifugal pumps operating in the range of very low specific speed. Two types of impellers, one equipped with six radial blades (Impeller A) and the other with four conventional backward-swept blades (Impeller B), are tested in a centrifugal pump operating at a non-dimensional specific-speed of $n_s=0.24$. Complex flow patterns captured by PIV are discussed in conjunction with the overall pump performance measured separately. It is revealed that Impeller A achieves higher effective head than Impeller B even though the flow patterns in Impeller A are more complex, exhibiting secondary flows and reverse flows in the impeller passage. It is shown that both the localized strong outward flow at the pressure side of each blade outlet and the strong outward through-flow along the suction side of each blade are responsible for the better head performance of Impeller A.